Industrial manufacturing facilities used for production of organic chemicals ranging from automobile wind shield fluid to agricultural pesticides generate millions of gallons of harmful liquid wastes everyday. These wastes are generally treated in wastewater treatment plants (WTPs) before they are discharged to receiving water bodies, so that they become harmless to the environment. Such plants generally consist of biological reactors, in which organic pollutants are used as food by microorganisms and converted to innocuous end products such as carbon dioxide and water. Due to their biological nature, these reactors are very sensitive to toxic substances that can enter the reactors through the influent wastewater. Such substances may inhibit or even completely arrest the biological activity in the reactors resulting in process upsets, and, consequently, in undesirable poor quality effluents. Unfortunately, the presence of such substances, especially when they are in low concentrations, is often undetected, and, therefore, prevention of introduction of these substances into the biological reactors is extremely difficult.
One of the most common ways to determine the inhibitory or toxic effects on biological activity in WTPs is by measuring the oxygen utilization or oxygen uptake rate (OUR) of the microorganisms in the biological reactors. Under normal operating conditions, a significant decrease in the OUR compared to normal levels is generally attributed to possible presence of inhibitory or toxic substances in the influent wastewater, whereas extremely high OURs reflect high biological activity. In extreme cases, OUR can instantaneously drop to zero indicating possible presence of highly toxic compound(s) in the influent. Caution should be exercised in interpreting low OUR results, because they can also be caused by low concentrations of organics in the influent. OURs are generally normalized by expressing them on the basis of unit weight of biomass. This is referred to as specific oxygen uptake rate (SOUR). Typical units for OUR and SOUR are: mg oxygen utilized/L/hour and mg oxygen utilized/g volatile suspended solids (VSS)/hour, respectively. (Note that VSS, typically expressed as g/L, is used as an indication of biomass concentration.)
The following laboratory procedure is generally used for measuring OUR:
1) Add an appropriate amount of wastewater sample to an active biomass culture from a biological reactor to form a sample mixture;
2) Measure the dissolved oxygen (DO) concentration of the mixture in a completely filled air-tight test vessel over a period of time; and
3) Calculate the OUR based on the decrease in the DO concentration of the sample mixture over the test period.
SOUR can be calculated by dividing the OUR value by the VSS concentration in the test system.
The OUR/SOUR test is thus done on a batch basis, therefore, a toxic substance can possibly enter the WTP during the time when the influent is not sampled for the laboratory test.
Another method to measure OUR is to use a submersible respirometer, such as the one described in U.S. Pat. No. 4,314,969. In this instrument, the aeration chamber of the respirometer is filled every 15-30 minutes with the wastewater, and the oxygen utilization measured by monitoring the decrease in the oxygen concentration in the air that is recirculated through the sample. In this respirometer, only the wastewater enters the aeration chamber with no provision specifically made for addition of already active and acclimated microorganisms. Also, the oxygen utilization is measured on a batch basis only every 15-30 minutes. Alternative to its use with the influent wastewater, the respirometer can also be used within the biological reactor of a WTP. However, in this case, even if the toxic effects are detected, it is only "after the fact"; the introduction of toxics into the reactor has already occurred, and, so, there is no opportunity for taking any preventive measure.
The apparatus and the method described in the invention presented here can be used (i) to detect the presence of inhibitory and toxic substances in the influents to the WTPs before they enter the biological reactors and (ii) to divert the influent flow to a temporary storage tank until such time when it is safe to feed the reactors again with the influent. This apparatus, which can be installed on line at the front end of a WTP, measures the OUR and SOUR of a given mixture of wastewater influent and active biomass that is already acclimated to the influent undergoing treatment, and prints out the results on a chart recorder. A warning alarm is given and/or the influent flow to the biological system is diverted to a temporary emergency storage tank, if dangerous levels of inhibitory or toxic substance(s) are indicated.
The apparatus proposed in this invention can also be used in association with full, pilot or laboratory scale biological reactors to:
1) determine whether increased loadings of organics in the influent (due to increase in the concentration and/or flowrate) compared to "normal" levels would be detrimental to process performance of biological reactors, thereby helping in terms of developing process control strategies;
2) investigate biological treatability and/or the effect on an existing biological reactor of a new waste stream or a test compound;
3) measure "endogenous" or background respiration rate of biomass from biological reactors; and
4) estimate, within a few minutes, organic loadings in terms of BOD.sub.5, 5-day Biochemical Oxygen Demand (Note: It takes five days to obtain BOD.sub.5 results), in the influents and effluents of biological reactors. In the case of full-scale WTPs, advance knowledge of influent and effluent BOD.sub.5 s can be used for process control and prevention of effluent permit violations, respectively.